A body of a vehicle such as an automobile includes various structural members. One of such structural members includes a bumper reinforcement (hereinafter, also referred to as a “BR”). A BR, which is also called as a bumper beam, is attached to a front part of the vehicle. The BR may also be attached to a rear part of the vehicle. This is for the purpose of bearing a load upon collision, thereby ensuring safety of humans in the vehicle. Typically, the BR is constituted by combining a panel made of a steel sheet and having a hat-shaped cross section with a closing plate (hereinafter, also referred to as a “CP”) which is made of a planar steel sheet. A flange part of the panel and the CP are superposed on each other, and the superposed part is joined by welding.
Both anti-collision performance and light-weightedness are demanded for the BR at the same time. In other words, improvement of energy absorption efficiency (EA/mass) is demanded for the BR. The energy absorption efficiency is a value obtained by dividing the absorbed energy of the BR by the weight of the BR. To cope with such demands, conventionally, there have been proposed BRs in which the shape of the panel having a hat-shaped cross section is advantageously contrived.
National Publication of International Patent Application No. 2007-521173 (Patent Literature 1) discloses a bumper beam which includes a panel having a reinforced part in a central area in its lengthwise direction. The reinforced part is provided in at least one flange part of the two flange parts. The reinforced part protrudes in a curved fashion from an edge of the flange part. Patent Literature 1 describes that providing the reinforced part in a part of the panel can improve energy absorption performance of the entire bumper beam.
Japanese Patent Application Publication No. 2011-219001 (Patent Literature 2) discloses a BR which includes a panel having a concave-shaped bead in a flange part. The concave-shaped bead makes up a passage which provides communication between the inside and outside of the BR. Patent Literature 2 describes that providing a bead in the flange part of the panel allows a coating liquid to flow into the BR at the time of production of a vehicle body, while ensuring strength of the BR.